(i) Field of the Invention
The present invention is directed to a substrate for a transfer mask which can be used in the manufacture of the transfer mask with apertures as the transfer portion of the mask, and a method for manufacturing the transfer mask by the use of the substrate.
(ii) Description of the Related Art
Recently, a drawing method has been suggested called partial batch exposure (also called block exposure or cell projection exposure), in electron beam lithography, which performs pattern exposure using electron beams. This method has risen suddenly into the spotlight as the next generation LSI technology because it has a short drawing time, is suited for mass production, and makes ultrafine pattern drawing possible (see Japanese Patent Application Laid-Open No. 81750/1985, etc.).
In partial batch exposure, a transfer mask, in which each type of aperture (through-hole) has been formed (a stencil mask) in the shape of the pattern that should be exposed onto a Si thin film which is tens of microns thick, is used, and a designated section (block or cell) is partially exposed in one batch which an electron beam passing through these apertures. By repeating the exposure while selecting the shape of the apertures and linking together partial patterns, the desired pattern is drawn.
The partial batch exposure drawing method was invented to solve the problems in the direct drawing methods (so called one-stoke drawing methods) already in practical use that draw by scanning an exposure pattern with a narrow beam spot of an electron beam. Such problems include extremely long drawing time and low throughput. Even compared to direct drawing methods using variable rectangles rapid drawing is possible.
Transfer masks used for such things as this kind of partial batch exposure have conventionally been produced with various methods, but in general are produced by processing a silicon substrate (such as the silicon wafers on the market) because of its workability and strength.
Concretely, as shown in FIG. 1 for example, a transfer mask 30 is produced by etch processing the rear surface of a silicon substrate 31, forming a support frame 32 and a thin film 33 supported by support frame 32, and forming apertures 34 in the thin film 33. In general, a wet etching process using inorganic or organic alkali aqueous solution is used for the rear surface processing of the silicon substrate, and a dry etching process is used to form the apertures because high precision is required.
Further, because etch processing is performed on both the front and rear surfaces of the substrate, in general a substrate with an etching stopper layer, at a designated depth within the substrate, is used for processing stability. For example, such substrates as a SOI (silicon on insulator) substrate in which two silicon substrates of differing thickness are stuck together with a SiO2 layer in between, a SIMOX (separation by implanted oxygen) substrate in which oxygen ions are driven in a high concentration onto a silicon substrate and an oxide film layer is formed by heat processing, or a multi-layered substrate formed with a boron rich layer at a designated depth on the silicon substrate as an etching stopper layer, are known as substrates with this kind of etching stopper layer.
When loaded on an electron beam drawing device for partial batch exposure, the size of the above transfer masks is between 5 mm-50 mm. This is small compared to the region of possible drawing of the drawing device used in the manufacture process of the transfer masks themselves. Therefore, recently large sized substrates have been used in the manufacture process of the transfer masks themselves, with the aim of improving manufacturing efficiency by patterning multiple transfer masks on a substrate at one time and processing them in one batch.
In this case, a dicing process is necessary in order to separate and remove each transfer mask from a single substrate.
However, the following problems exist in the conventional method of manufacture of transfer masks.
First, it is difficult to plan shorter TAT (turn around time). TAT stands for one cycle of operations, i.e. from designing the device pattern, trial production of a transfer mask, trial production of a LSI chip, changes to the design specifications, to production of the transfer mask. While stencil masks are now in the stage of practical use, the biggest problem is reducing the TAT. So-called hybrid lithography means that stencil masks are used in pattern transfers of 0.25 xcexcm or less in super LSI, while conventional photomasks are used in other pattern transfers. If the manufacturing time of the stencil masks is longer than the manufacturing time of the photomasks, supply of the stencil masks becomes a source of delay in the whole process. When aiming for TAT reduction, it is absolutely necessary to make the manufacturing time of the stencil masks equivalent to the manufacturing time of the photomasks.
The manufacture of stencil masks is difficult compared to the manufacture of photomasks and such, because formation of a thin film and apertures is necessary. It is difficult to reduce the manufacturing time because there are many processes of manufacture, and there is a high rate of defect generation.
The present invention has been created with consideration given to the problems mentioned above, and aims to solve such conventional problems by providing a substrate for a transfer mask and a method for manufacturing a transfer mask with a short manufacturing time that will reduce TAT.
In order to achieve the above aims, the substrate for transfer masks of the present invention has apertures formed in the thin film supported by a supported frame, and has at least one alignment mark formed on the substrate in advance which is used for the purpose of processing a designated location on the substrate.
In a further invention the substrate for transfer masks of the present invention has apertures formed in the thin film supported by a supporting frame, has a rear surface concavity formed in advance on the rear surface of the substrate, and has a dry etching stopper layer on the rear surface of the thin film.
In another invention, in the substrate for transfer masks of the present invention, the rear surface concavity is filled with one or more selected from the group consisting of a resin, an adhesive, a paste and a low-melting metal;
a plate is affixed to the rear surface of the substrate for transfer masks with one or more selected from the group consisting of a resin, an adhesive, a paste and a low-melting metal;
the above plate is composed of one or more selected from the group consisting of silicon, carbon, a metal and a glass;
a dry etching mask layer is laid on the front surface of the substrate for transfer masks for the purpose of forming an aperture pattern in advance;
a slit for cutting is formed in advance in the rear surface side of the substrate for transfer masks for the purpose of dividing each transfer mark formed in a multiple arrangement on a single substrate;
the cutting slit is filled with one or more selected from the group consisting of a resin, an adhesive, a paste and a low-melting metal; or
at least one alignment mark is build in advance onto the substrate used for the purpose of processing a designated location on the front surface of the substrate for transfer masks.
The method of manufacture of transfer masks of the present invention uses the substrate for transfer masks of the present invention.
With the present invention, the production time of transfer masks after receipt of the aperture pattern design can be easily reduced, and a reduction in TAT can be achieved by finishing processing of the rear surface concavity (back etching) in advance.
Further, by performing such difficult processes as forming a thin film in advance, one can avoid the generation of defects through these processes. When defects are generated, lower costs and improved efficiency can be promoted by not performing aperture formation.
In addition, because the substrate for transfer masks of the present invention is structurally stable, defects such as damage will not arise in the manufacture process of the transfer masks, and the transfer masks can be manufactured without many steps.